In contemporary WDM optical networks, an essential building block is a device that can separate a multi-wavelength optical signal into multiple spectral channels and subsequently route the spectral channels into multiple output ports in a dynamically reconfigurable fashion. Such a device can be used to construct dynamic optical add-drop multiplexers (OADMs), optical multiplexers/demultiplexers, and optical cross-connects.
One type of wavelength separating and routing device includes an array of fiber collimators serving as one or more input ports and one or more output ports; a wavelength-separator; a beam-focuser; and an array of channel micromirrors. This type of wavelength separating and routing device is described for example in U.S. patent application Ser. Nos. 09/938,426, 10/005,714, 10/060,493 (now issued as U.S. Pat. No. 6,549,699), 10/076,145, and 10/143,651, all of which are assigned to the present assignee and incorporated herein by reference. In operation, a multi-wavelength optical signal emerges from an input port. The wavelength-separator separates the multi-wavelength optical signal into multiple spectral channels, each characterized by a distinct center wavelength and associated bandwidth. The beam-focuser focuses the spectral channels into corresponding focused spots. The channel micromirrors may be positioned such that each channel micromirror receives a unique one of the spectral channels. The channel micromirrors may also be individually controllable and movable (e.g., pivotable or rotatable), so as to reflect the spectral channels into selected output ports. As such, each channel micromirror may be assigned to a specific spectral channel, hence the name “channel micromirror”. Each output port may receive any number of the reflected spectral channels.
Because the operation of such an optical system is dependent on the position of the channel micromirrors, it would be desirable to provide micromirror position sensing units for use in these types of optical systems. Particularly, it would be very useful to monitor the positions of the channel micromirrors in order to facilitate control of multiple spectral channels coupled into the output ports on a channel-by-channel basis and in a dynamic (or real-time) fashion.